This invention relates to an improvement in a process for leaching of metal from metal sulfide minerals using an oxidative leaching solution, i.e., a leaching solution containing an oxidizing agent.
In the mining industry there has been a recent trend toward an increased use of chemical leaching techniques. Most leaching processes are slow and usually recovery of metal is incomplete. Generally, in leaching ores the leaching process is terminated when the rate of extraction of metal from the ore becomes too slow for further leaching to be economically feasible. For a variety of reasons leaching is often terminated at 50-85% of metal recovery. Some of the problems which cause this termination include coating of the ore particles with deposits of sulfur, precipitated ferric salts, or other materials which hinder leaching; clogging of access pores in the body of ore thereby slowing or stopping diffusion of leaching solution into the ore particles; and physical problems, such as channeling.
The leaching of metal sulfide minerals with ferric chloride and ferric sulfate solutions is well-known in the art. For example, U.S. Pat. No. 1,588,806 issued to Pike et al. on June 15, 1926 discloses leaching of metals from sulfide ores by using ferric sulfate or preferably ferric chloride.
In "Advanced Chemical Processing of Copper Sulfide Concentrates", a research proposal submitted to the National Science Foundation in November, 1972, the use of hydrogen peroxide to oxidize chalcopyrite at room temperature is disclosed. Stabilized forms of hydrogen peroxide were disclosed to be more effective in dissolving chalcopyrite then sulfuric acid and unstabilized hydrogen peroxide.
M. I. Timerbulatova et al., "The Use of Hydrogen Peroxide for the Separate Determination of Primary and Secondary Copper Sulfides" in Metody Izucheniya Veshchestvennogo Sostava i ikh Primenenie, 1965, pp. 113-117, disclose the dissolution of copper minerals with excess hydrogen peroxide. Complete dissolution of copper from finely ground chalcopyrite was obtained with a large excess of hydrogen peroxide, i.e., a solution containing 15% by weight hydrogen peroxide at a pH of 4.5.
In spite of these prior art methods, the efficient use of hydrogen peroxide to leach metal sulfide minerals remains to be demonstrated.